1. Field of the Invention
Exemplary embodiments of the invention relate to a backlight module, and more particularly, to a direct-under type backlight module used in a liquid crystal display.
2. Description of the Related Art
Liquid crystal display has been used in notebook personal computers, office automatic equipments, audio/video equipments, etc. because of advantages such as miniaturization, thin profile, and low power consumption.
The liquid crystal display includes a liquid crystal display module and a backlight module. The backlight module may be classified into an edge type backlight module and a direct-under type backlight module depending on a location of a light source.
In the edge type backlight module, a light source is positioned around an edge of a light guide plate. While light produced by the light source is repeatedly reflected inside the light guide plate, the light is emitted to the liquid crystal display module through a main surface of the light guide plate.
In the direct-under type backlight module, a plurality of light sources is parallelly positioned under the liquid crystal display module, a reflective plate is positioned under the light sources, and a diffuser plate is positioned on the light sources. Light produced by the light sources is emitted to the liquid crystal display module through the diffuser plate.
Because the number of light sources in the direct-under type backlight module increases as compared with the number of light sources in the edge type backlight module, the direct-under type backlight module can achieve a high luminance of an image.
However, in the direct-under type backlight module, because the light sources are parallelly positioned at a constant distance therebetween, the luminance of the image just above the light sources is high, but the luminance of the image on a space between the light sources is low. Accordingly, the non-uniformity of luminance periodically occurs in the direct-under type backlight module, and thus the non-uniformity of display occurs on a display screen of the liquid crystal display module.
In the related art direct-under type backlight module, an air gap is thickly formed so as to solve the problems of the non-uniformity. However, the thick air gap causes a reduction in a degree of freedom in a combination of optical sheets of the direct-under type backlight module.
In other words, in case the air gap is thickly formed, the diffuser plate has to be positioned in a lowest portion of the optical sheet closest to the light source because a diffuser sheet and a prism sheet do not have a self bearing power.
Another method for solving the non-uniformity of luminance is to reduce the distance between the light sources. However, because the method causes an increase of the number of light, the manufacturing cost and the power consumption increased and a process for manufacturing the backlight module is complicated.